1. Field of the Invention
The present invention relates to an endless belt, a belt conveyor provided with the belt and an image forming apparatus provided with the belt and particularly to an endless belt comprising an endless belt body formed by inflation molding, a belt conveyor provided with the belt and an image forming apparatus provided with the belt.
2. Description of the Related Art
A known image forming apparatus such as a printer transfers toner images on photoconductive drums to an intermediate transfer belt (primary transfer), subsequently transfers toner images on the intermediate transfer belt (belt) to a sheet in a nip portion between the intermediate transfer belt and a secondary transfer roller at once (secondary transfer), and then forms an image on the sheet (see, for example, Japanese Unexamined Patent Publication No. H11-59962).
The above intermediate transfer belt is generally endless and formed by inflation molding. FIG. 5 is a schematic diagram of an extruder showing a method for forming an intermediate transfer belt by inflation molding using the extruder. In this forming method, as shown in FIG. 5, a raw material 2 poured into the extruder 1 is cooled by cooling air 4 while being extruded through a die 3 of the extruder 1. In this way, a tubular body 5a solidified to a certain extent as shown in FIG. 6 is formed. Subsequently, the tubular body 5a is squeezed flat as shown in FIG. 7 by a pair of pinch rollers 6 at the top of the extruder 1, and the both longitudinal sides of the tubular body 5a are folded. Then, a squeezed tubular body 5b is concentrically taken up. An intermediate transfer belt is obtained by cutting the above taken-up tubular body 5b to a specified length in a take-up direction. This specified length is the width of the intermediate transfer belt.
The intermediate transfer belt formed by inflation molding in this way has folds at two positions in a rotating direction of the intermediate transfer belt corresponding to the opposite ends of the flat tubular body 5b. These folds become folded traces which is finally unnoticeable in appearance after a heating process and the like.
However, the above folded traces are thinner than the other portions of the intermediate transfer belt when they are formed and, accordingly, have lower strength. Thus, upon driving the extended intermediate transfer belt, cracks are likely to occur at one of the opposite ends of the folded traces of the intermediate transfer belt due to various loads such as tensile stresses and bending stresses acting on the intermediate transfer belt. Therefore, there has been a demand for improving the durability of the intermediate transfer belt.